RU2426195C1 - Photoelectric converter, imaging system - Google Patents

Abstract

FIELD: physics.

SUBSTANCE: proposed converter comprises multiple photo electric converters with light-sensitive surface, isolating films, multiple light guide sections arranged atop isolating films. Note here that each light guide section directs light onto light-sensitive surface and boundary sections. Note also that each boundary section forms boundary between adjacent light guide sections and is made from material with lower refractivity compared with that of light guide section material. Note also that width of each boundary section does not exceed half the minimum wavelength of visible light, and height from bottom to top surfaces of every light guide section makes at least double maximum wavelength of visible light.

EFFECT: efficient light collection.

15 cl, 9 dwg

Description

FIELD OF THE INVENTION

The present invention relates to a photoelectric conversion device and an imaging system.

State of the art

A photoelectric conversion device is necessary for efficiently collecting incident light on the photosensitive surface of the photoelectric conversion element. In the semiconductor image pickup device disclosed in Japanese Patent Laid-open No. 06-224398, an intermediate polymer layer is disposed between the microlens and the photosensitive surface of the photoelectric conversion element, as shown in FIG. 1 in Japanese Laid-open Patent Application No. 06-224398. A layer having a lower refractive index than the intermediate layer is located between the intermediate layer and the transmitting electrode for transferring charges of the photoelectric conversion element. According to Japanese Patent Application Laid-open No. 06-224398, obliquely incident light that is not involved in the photoelectric conversion in the conventional technique can be transmitted to the photosensitive surface of the photoelectric conversion element by using full reflection at the interface between the intermediate layer and the low refractive index layer.

However, the semiconductor image pickup device in Japanese Patent Laid-open No. 06-224398 does not examine light entering the boundary region between an intermediate layer of a predetermined pixel and an intermediate layer of a pixel adjacent to a predetermined pixel. For example, when light propagating perpendicular to the photosensitive surface of the photoelectric conversion element enters the boundary region between the intermediate layer of a predetermined pixel and the intermediate layer of a pixel adjacent to a predetermined pixel, it is difficult to direct light onto the photosensitive surface of the photoelectric conversion element.

With a decrease in the area of the pixel, including the photoelectric conversion element, the ratio of the area of the boundary region to the area of the pixel increases. Light entering the boundary region cannot be ignored.

Disclosure of invention

An object of the present invention is to efficiently collect light entering a photoelectric conversion device on a photosensitive surface of a photoelectric conversion element in a photoelectric conversion device.

According to a first embodiment of the present invention, the photoelectric conversion device is characterized in that it comprises: a plurality of photoelectric conversion elements, each of which has a photosensitive surface; insulating films placed on a plurality of photoelectric conversion elements; a plurality of light guide portions arranged on top of the insulating films, each of the plurality of light guide portions directing light onto the photosensitive surface of each of the plurality of photoelectric conversion elements; and boundary sections, wherein each of the boundary sections forms a boundary between adjacent light guide sections and is made of a material having a lower refractive index than the material of which the plurality of light guide sections consists, in which the width of each of the boundary sections does not exceed half the smallest wavelength in the range of wavelengths of visible light, and the height from the lower surface to the upper surface of each of the many light guide sections is not less than twice the largest wavelength in the wavelength range n of visible light.

According to a second embodiment of the present invention, the photoelectric conversion device is characterized in that it comprises: a plurality of photoelectric conversion elements, each of which has a photosensitive surface; insulating films placed on a plurality of photoelectric conversion elements; a plurality of light guide sections arranged on top of insulating films of several layers, each of the many light guide sections directing light to the photosensitive surface of each of the plurality of photoelectric conversion elements; and boundary sections, wherein each of the boundary sections forms a boundary between adjacent light guide sections and is made of a material having a lower refractive index than the material of which the plurality of light guide sections consists, in which the width of each of the boundary sections does not exceed half the smallest wavelength in the range of wavelengths of visible light, and the height from the lower surface to the upper surface of each of the many light guide sections is not less than four times the width of each of the boundary sections.

According to a third embodiment of the present invention, the image forming system is characterized in that it comprises: a photoelectric conversion device according to the first or second embodiment of the present invention; an optical system that forms an image on the image perception plane of the photoelectric conversion element; and a signal processing unit that processes the signal output from the photoelectric conversion device to generate image data.

According to the present invention, it is possible to efficiently collect light entering the photoelectric conversion device on the photosensitive surface of the photoelectric conversion element in the photoelectric conversion device.

Further features of the present invention will be apparent from the following description of illustrative embodiments given with reference to the accompanying drawings.

Brief Description of the Drawings

FIG. 1 is a sectional view of a photoelectric conversion device according to a first embodiment.

Figure 2 includes 2A and 2B are graphs explaining the behavior of light in the photoelectric conversion device according to the first embodiment.

Figure 3 is a view explaining the behavior of light in the photoelectric conversion device according to the first embodiment.

4 is a graph showing the relationship between the height of the light guide section, the gap between the light guide sections and the light collection coefficient.

5 is a sectional view of a photoelectric conversion device according to a second embodiment.

6 is a plan view of a photoelectric conversion device according to a second embodiment.

7 includes 7A-7F sectional views illustrating manufacturing steps of a photoelectric conversion device according to a second embodiment.

Fig. 8 is a sectional view of a photoelectric conversion device according to a third embodiment.

9 is a block diagram for explaining an image forming system.

The implementation of the invention

Distinctive features of the present invention are the structure of the light guide section and the relative position of the light guide section and other light guide sections adjacent to the light guide section, the light guide sections being arranged in accordance with each photoelectric conversion element in a photoelectric conversion device having a plurality of photoelectric conversion elements.

In particular, the present invention is characterized in that the gap between adjacent light guide sections (i.e., the width of the boundary portion) is set so that it does not exceed half the smallest wavelength in the wavelength range of visible light, and the height of the light guide section is set so that it was no less than twice the largest wavelength in the wavelength range of visible light. This structure can effectively direct (or collect) the light entering the boundary portion onto the photosensitive surface of the photoelectric conversion element, and thus increase the light collection coefficient expressing the ratio of the light directed to the photosensitive surface of the photoelectric conversion element, to the light entering photoelectric conversion device.

Visible light is also called the visible spectrum, and it is formed by electromagnetic waves in the range of visible electromagnetic spectra. The wavelength of visible light usually ranges from 400 nm (inclusive) to 750 nm (inclusive). See "Dictionary of Technical Terms of Optics, 3rd ed." (Handbook of Technical Terms in Optics, 3rd edition), Optoelectronics in the wavelength range of visible light.

In this description of the invention, the term "wavelength range of visible light" also means the wavelength range of the light components passing through color filters (e.g., red, green, and blue primary filters) arranged in accordance with the respective photoelectric conversion elements. In this case, "the smallest wavelength in the wavelength range of visible light" means the wavelength (for example, the wavelength of blue light) specified by the spectral distribution of transmission of the color filter, the color corresponding to the smallest wavelength among the colors specified by color filters, in the photoelectric conversion device . "Longest wavelength in the wavelength range of visible light" means a wavelength (e.g., a red light wavelength) specified by a spectral distribution of transmission of a color filter, a color corresponding to the longest wavelength among the colors specified by color filters, in the photoelectric conversion device.

Other terms used in the description of the invention will also be explained.

A pixel is a minimal module that includes a photoelectric conversion element. The pixel may include the aforementioned color filter, a transistor, and the like, in addition to the photoelectric conversion element.

A “substrate” is a semiconductor substrate serving as a base material, but may also include a substrate material processed as follows. For example, a substrate even means an element in which one or a plurality of semiconductor regions and the like are formed, an element subjected to a series of production processes, or an element subjected to a series of production processes.

The present invention will be described in detail with reference to the accompanying drawings.

(First Embodiment)

1 is a cross-sectional view of a photoelectric conversion device 1 according to a first embodiment. The light guide sections are arranged on a plurality of photoelectric conversion elements in accordance with the respective photoelectric conversion elements. The gap between adjacent light guide sections (i.e., the width of the boundary section) and the height of the light guide section are set equal to predetermined values.

1, a substrate 100 includes a channel 101 and photoelectric conversion elements 102. The substrate 100 is made, for example, of silicon.

Channel 101 contains an impurity of the first type of conductivity (for example, P-type) with a lower concentration than in the photoelectric conversion element 102.

The photoelectric conversion element 102 contains an admixture of a second type of conductivity (for example, N-type), which corresponds to the carrier, in a higher concentration than channel 101. The second type of conductivity has a conductivity type opposite to the first type of conductivity.

The photoelectric conversion element 102 has a photosensitive surface 103. A plurality of photoelectric conversion elements 102 are disposed in the substrate 100. Each photoelectric conversion element 102 performs photoelectric conversion in a barrier layer formed near the boundary between the photoelectric conversion element 102 and the channel 101, generating and accumulating charges in accordance with light incident on the photosensitive surface 103.

Multiple-layer insulating films 104a and 104b are disposed on photoelectric conversion elements 102. An insulating film 104a isolates the surface of the substrate 100 from the wiring layer 105 (described below). The insulating film 104b isolates the layer thereon from the wiring layer 105. Each of the insulating films 104a and 104b is made, for example, in the form of a film of silicon oxide.

The wiring layer 105 is located between the insulating films 104a and 104b. The wiring layer 105 is made, for example, of an intermetallic compound containing mainly aluminum.

A plurality of light guide sections 106 are formed on the insulating film 104b in accordance with the respective photoelectric conversion elements 102. The material forming the light guide portion 106 is, for example, silicon oxide, and air fills the boundary portion 107 between adjacent light guide portions. In this structure, light entering the light guide portion 106 from the upper surface 106a of the light guide portion 106 easily experiences full reflection by the side surface 106c serving as an interface between the light guide portion 106 and the boundary portion 107, and is directed to the lower surface 106b. When the refractive indices of the light guide portion 106 and the insulating film 104b are almost equal to each other, light is hardly reflected at the interface between them. Therefore, the light directed to the bottom surface 106b easily reaches the photosensitive surface 103 of the photoelectric conversion element 102 through the insulating films 104a and 104b.

The height H of each light guide portion 106 is set so that it is not less than twice the largest wavelength in the wavelength range of visible light. The gap W between two adjacent light guide sections 106 (i.e., the width W of the boundary portion 107) is set so that it does not exceed half the smallest wavelength in the wavelength range of visible light. In such a structure, the light entering the region (boundary section) where there are no light guide sections is refracted to the center of the light guide section and easily enters the light guide section from its side surface. As described above, the light entering the light guide portion is easily guided to the photosensitive surface of the photoelectric conversion element. This makes it possible to increase the light collection coefficient expressing the ratio of the light directed to the photosensitive surface of the photoelectric conversion element to the light entering the photoelectric conversion device 1.

According to figure 1, the height H of the light guide section 106 is set so that it is not less than twice (for example, 1.5 μm) of the largest wavelength in the wavelength range of visible light. The gap W between adjacent light guide sections 106 (i.e., the width W of the boundary portion 107) is set so that it does not exceed half (for example, 200 nm) of the smallest wavelength in the wavelength range of visible light. The height H of the light guide portion 106, the width W of the boundary portion 107 and the wavelength of the collected light will be described in detail below.

FIG. 2, including 2A and 2B, shows the results of modeling the behavior of light in the photoelectric conversion device 1, according to the first embodiment. In particular, 2A of FIG. 2 shows the result of an analysis of the behavior of light when light enters the upper surface of the light guide portion perpendicularly (at an angle of incidence of 0 °). 2B of FIG. 2 shows the result of analyzing the behavior of light when light enters the upper surface of the light guide portion obliquely (at an angle of incidence of 20 °).

In the simulation, the parallel wavelength was 500 nm, the height H of the light guide section was 5.0 μm, and the gap W between adjacent light guide sections 106 (i.e., the width W of the boundary section 107) was 250 nm.

2A and 2B of FIG. 2, a rectangular screen 200 on a black background displays a simulation result. Black and white stripes on the screen 200 display the behavior of light. Deeper gradations of black and white mean that the amplitude of the light wave increases, and the energy of light, expressed by the square of the amplitude, increases. The gray section shows the center of amplitude and means that the light energy is small.

2A of FIG. 2 shows a case where parallel light components arrive at the upper surface of the light guide portion at an angle of incidence of 0 °. 2B shows a case where parallel components of the light enter the upper surface of the light guide portion at an angle of incidence of 20 °. The contour arrows in 2A and 2B of FIG. 2 schematically explain the behavior of the incident light as a function of the difference in the angle of incidence.

In 2A of FIG. 2, the parallel light component, indicated by arrow 203 and arriving near the center of the light guide portion 201, propagates through the light guide portion almost perpendicular to the photosensitive surface of the photoelectric conversion element. The parallel light component, indicated by arrow 204 and entering the boundary portion between the light guide portion 201 and the light guide portion 202, is refracted by the lateral surface of the light guide portion 201 (i.e., the interface between the light guide portion and the boundary portion) in accordance with the difference between the refractive indices of the light guide portion 201 (silicon oxide) and the boundary portion (air), enters the light guide portion 201 and propagates through the light guide portion 201 to the center on the lower surface of the light guide ka 201, as indicated by arrow 205.

2B of FIG. 2, the parallel component of light 208, which enters the light guide section 206 at an angle of incidence of 20 °, is completely reflected by the side surface of the light guide section 206, and extends to the center on the lower surface of the light guide section 206, as shown by arrow 210. Similar to the behavior on 2A of FIG. 2, the parallel light component 209 entering the boundary portion between the light guide portion 206 and the light guide portion 207 is refracted by the lateral surface of the light guide portion 206 (i.e., the interface between the light guide portion and the boundary portion) in accordance with the difference between the refractive indices of the light guide portion 206 (silicon oxide) and the boundary portion (air), enters the light guide portion 206 and extends to the center on the lower surface of the light guide portion 206, as indicated by arrow 210.

In a conventional photoelectric conversion device, when light enters the boundary region between adjacent lenses in a microlens lens array arranged in two dimensions in accordance with photoelectric conversion elements 102, the light is often linearly distributed. Therefore, it is difficult to direct the light entering the boundary region on the lens matrix to the photosensitive surface of the photoelectric conversion element.

In contrast, in the photoelectric conversion device 1 according to the first embodiment, the light entering the boundary portion between adjacent light guide sections is refracted by the side surface of the light guide portion (i.e., the interface between the light guide portion and the boundary portion), enters the light guide portion, and is easily sent to the photosensitive surface of the photoelectric conversion element. Thus, it is easy to direct the light arriving at the boundary portion between adjacent light guide sections to the photosensitive surface of the photoelectric conversion element. Compared to a conventional photoelectric conversion device, the photoelectric conversion device 1 can increase the light collection coefficient expressing the ratio of the light directed to the photosensitive surface of the photoelectric conversion element to the light entering the photoelectric conversion device 1.

The behavior of the light in the light guide section will be described in detail with reference to FIG. Figure 3 shows a view explaining the principle of collecting light when parallel components of the light enter the boundary section between adjacent light guide sections. The same positions as in FIG. 1 indicate parts having the same functions.

In FIG. 3, two light guide sections 106 for convenience are distinguished as light guide sections 106-1 and 106-2. 3, point sources 302, 303, and 304 represent light components immediately after parallel light components 301 arrive at the light guide portion 106-1, the boundary portion 107, and the light guide portion 106-2, respectively. Many light guide sections 106-1 and 106-2 are adjacent to each other. The point sources 302 and 304 are located in the light guide sections 106-1 and 106-2, while the point source 303 is located in the boundary portion (gap) 107 between the light guide sections 106-1 and 106-2. In this case, the width of the boundary portion 107, i.e. the gap between the light guide sections 106-1 and 106-2 is set so that it does not exceed half the wavelength of the incident parallel component 301 of the light, and does not exceed half the smallest wavelength in the wavelength range of visible light. The height of each of the light guide sections 106-1 and 106-2 is set so that it is not less than twice the largest wavelength in the wavelength range of visible light. For ease of explanation, consider one light guide portion 106-1.

The light beam 308, reaching the boundary portion 107, propagates almost rectilinearly. However, the light beam 307 enters the side surface 106c-1 of the light guide portion 106-1 at an angle. The light beam 307 is refracted by the side surface 106c-1 of the light guide section 106-1, enters the light guide section 106-1, and extends to the center on the lower surface 106b-1 of the light guide section 106-1.

In contrast, most light rays 305 and 306 entering the light guide section 106-1 are completely reflected by the side surface 106c-1 of the light guide section 106-1, since the refractive indices of the light guide section 106-1 and the boundary section 107 are different from each other (in particular, the refractive index of the light guide portion 106-1 is higher than the refractive index of the boundary portion 107), so light rarely arrives at the boundary portion 107. Since light hardly arrives at the boundary portion 107, there are few light rays that amplify the light beam 308, propagating rectilinearly through the boundary portion 107. Since most of the light rays propagating through the boundary portion 107 enters the light guide portion 106-1 or 106-2, the energy 308 of the beam of light propagating through the boundary portion 107 ultimately decreases. Thus, most of the light entering the boundary portion 107 is collected in the light guide portion.

4 is a graph showing the relationship between the height of the light guide section, the gap between the light guide sections (i.e., the width of the boundary section) and the light collection coefficient. The graph in FIG. 4 is obtained by the same simulation as in FIGS. 2A and 2B. Figure 4 shows the light collection coefficient depending on the height of the light guide section when the wavelength of the incident light is set to 500 nm, and the gap between adjacent light guide sections (i.e., the width of the boundary section) is set to 0.25 μm, 0.5 μm, 0.75 μm and 1.0 μm. The abscissa axis of the graph displays the value of the length reduced to the wavelength when the upper surface 106a (see FIG. 1) of the light guide portion is defined as a reference point in the direction perpendicular to the substrate, and the direction of the substrate in which the light propagates is set as a positive direction. In other words, the abscissa axis represents the position (the optical distance from the position at the same level with the upper surface 106a of the light guide section) at the boundary section. The ordinate axis displays the reduced value of the light energy remaining at the boundary portion between adjacent light guide sections when the light energy at the position of the boundary portion that is at the same level as the surface of the light guide section is set to 1. As described above, the decrease in the light energy remaining at the boundary section between adjacent light guide sections means that most of the light at the boundary section is collected in the light guide sections.

According to FIG. 4, when the position at the boundary portion between the light guide portions moves from the position at the same level as the surface of the light guide portion, the light energy at the position at the boundary portion decreases, while the gap between the light guide portions remains constant. In Fig. 4, the light energy when light propagates at a distance of two wavelengths ("2" on the abscissa axis) through a boundary portion corresponding to a gap of 1.0 μm between the light guide portions is compared with light energy when light propagates at a distance of two wavelengths through the boundary section corresponding to a gap of 0.25 μm between the light guide sections. The light energy is reduced to about 70% at the boundary portion corresponding to a gap of 1.0 μm between the light guide sections, and about 10% at the boundary portion corresponding to a gap of 0.25 μm between them.

In particular, about 30% of the light entering the boundary portion corresponding to a gap of 1.0 μm between the light guide portions enters the light guide portions. In contrast, about 90% of the light entering the boundary portion corresponding to a gap of 0.25 μm between the light guide portions enters the light guide portions. This means that the light collection coefficient is higher for a narrower gap between the light guide sections (smaller width of the boundary section). In addition, even after the light travels a distance 10 times the wavelength, 20% of the light energy remains when the gap between the light guide portions is 1.0 μm. Thus, the same effects that are obtained when the gap between the light guide sections is 0.25 μm are not achieved.

Based on these results, the light collection coefficient increases significantly when the gap between the light guide sections is equal to half the wavelength (i.e. 0.5λ), and it is sufficient to set the height (i.e. 2λ) of the light guide section so that it is not less than four times the gap between the light guide sections. In addition, the light collection coefficient can be increased by making the gap between the light guide portions shorter with respect to the wavelength and by making the light guide portion higher. If there is a distribution along the wavelength, as in visible light, it is more desirable to make the gap between the light guide sections not exceeding half the smallest wavelength in the wavelength range of visible light and make the height of the light guide section not less than twice the largest wavelength in the wavelength range of visible light. This structure allows to achieve a satisfactory light collection effect for all light components in the wavelength range of visible light. Since it is not necessary to form a complex shape to increase the light collection coefficient, the manufacturing process is simplified, and the shape control is also simplified.

In the aforementioned wavelength range of visible light, the shortest wavelength is 400 nm and the longest wavelength is 750 nm. In this case, it is sufficient that the gap between the light guide sections (i.e., the width of the boundary section) is not more than 0.2 μm and that the height of the light guide section is not less than 1.5 μm. For example, the light guide sections are formed with a gap of about 0.2 μm between the light guide sections (i.e., a boundary section with a width of about 0.2 μm is formed) and the height of the light guide section is about 1.5 μm. A photoelectric conversion device 1 having light guide sections that increases the light collection coefficient of visible light can be used, in particular, as a photoelectric conversion device for visible light. In this case, it is desirable to form the photoelectric conversion element so that it has a spectral sensitivity corresponding to visible light.

The wavelength range of the light actually entering the photoelectric conversion device 1 can be predicted to some extent (for example, it is determined by the wavelength passing through the color filter). Thus, the gap between the light guide sections and the height of the light guide section can also be designed based on the wavelength range of the light source. For example, several light sources (wavelengths passing through the filter) are assumed, and the gap between the light guide sections and the height are selected so as to cover the wavelength ranges of the light rays from these light sources.

The largest and smallest wavelengths that determine the height of the light guide section and the gap between the light guide sections can also be determined using the wavelength range of visible light, as described above, and can also be determined as follows. For example, the gap between the light guide sections and the height of the light guide section can also be determined based on the distribution of spectral sensitivity (photoelectric conversion efficiency with respect to the incident light wavelength) of the photoelectric conversion element.

For example, the lower limit value of the spectral sensitivity is determined, which is acceptable in the distribution of the spectral sensitivity of the photoelectric conversion element. Accordingly, you can set the upper limit (from the infrared range) and the lower limit (from the ultraviolet range) of the wavelength.

For example, when the spectral sensitivity of the photoelectric conversion element has a peak, the wavelengths on the upper and lower limits of the wavelength range, when the light intensity reaches half the peak value i, can also be used. The wavelengths at the upper and lower limits of the wavelength range, when the light intensity reaches half the peak value, are the wavelengths at the lower and upper limits when the full width is obtained at half maximum. The spectral sensitivity of the photoelectric conversion element can be appropriately determined depending on the type of semiconductor that forms the photoelectric conversion element, the manufacturing method, and the like. The light guide sections defined in the above manner can efficiently collect light corresponding to a peak of sensitivity of the photoelectric conversion element.

When color filters are designed to decompose light according to wavelengths and perform photoelectric conversion in each pixel, the wavelength range of incident light can be estimated and determined from the transmission spectrum (the intensity of light passing through the color filter with respect to each wavelength) of the color filter. For the photoelectric conversion device 1 having color filters of the primary colors, it is sufficient to select the shortest wavelength in the wavelength range of visible light from the transmission spectrum of the blue filter, and the longest wavelength from the transmission spectrum of the red filter. For example, the longest wavelength can be selected from the wavelengths at which light shows an intensity of half the peak value in the transmission spectrum of the red filter. The smallest wavelength can be selected from the wavelengths at which light exhibits an intensity of half the peak value in the transmission spectrum of the blue filter. A wavelength at which light exhibits a peak intensity may also be selected. The wavelength can also be set by combining the spectral sensitivity of the photoelectric conversion element and the spectral transmittance of the color filter. By setting the wavelength in this way, it is possible to efficiently collect light corresponding to the peak of sensitivity of the photoelectric conversion element.

In the photoelectric conversion device 1 according to the first embodiment, the light entering the region (boundary portion) where there are no light guide sections enters the light guide section from its side surface, propagates to the center of the lower surface, and is directed toward the photosensitive surface of the photoelectric conversion element, increasing light collection coefficient. In the first embodiment, air fills the space between the light guide sections, but it is also possible to place material having a lower refractive index than the light guide section. The material of the light guide portion is not limited to the above.

In the first embodiment, a multilayer interconnect structure made of insulating films of several layers and a wiring layer is described. However, the first embodiment is also applicable to the structure of the CCD-based photoelectric conversion device or the like, or to the structure in which the light guide portion is arranged on the transparent electrode.

(Second Embodiment)

The photoelectric conversion device 5 according to the second embodiment has a lens matrix and a color filter matrix corresponding to the lens matrix. Each color filter of the color filter matrix is included in the light guide portion, in addition to the structure of the first embodiment. FIG. 5 is a cross-sectional view of the photoelectric conversion device 5 according to the second embodiment, and FIG. 6 is a top view of the photoelectric conversion device 5. The same positions as in FIG. 1 indicate the same details, and we will not repeat their description.

5, lenses 501 are located between the light guide portions 505 and the insulating film 104b. The plurality of lenses 501 forms a two-dimensional array in accordance with the respective photoelectric conversion elements 102.

Each light guide portion 505 includes a color filter 503. By positioning the lens 501 between the light guide portion 505 and the insulating film 104b, the light collected by the light guide portion 505 can be efficiently collected on the photosensitive surface 103 of the photoelectric conversion element. Since the light guide portion 505 includes a color filter 503, the color filter 503 can be accommodated without increasing the height of the photoelectric conversion device 5 from the photosensitive surface 103. In other words, the distance between the photosensitive surface 103 and the color filter 503 in the photoelectric conversion device 5 can be reduced.

It is desirable to form the color filter 503 from a material having the same refractive index as the lower portion 502 and the upper portion 504 of the light guide portion 505. This ratio of refractive indices reduces the reflection of light at the interface between the color filter 503 and the lower portion 502 or the upper portion 504 of the light guide plot.

The side surface 503c of the color filter 503 preferably forms a surface extending from the side surface 502c of the lower portion 502 of the light guide portion 505 and the side surface 504c of the upper portion 504.

If the side surface of the color filter protrudes into the light guide portion from the side surfaces of the upper and lower portions of the light guide portion, even light entering the light guide portion 505 may not pass through the color filter 503, reducing color sensitivity. The lateral surface of the color filter protrudes into the light guide portion from the side surfaces of the upper and lower portions of the light guide portion when the color filter is smaller in transverse width than the upper surface or lower surface of the light guide portion when viewed from above (in a direction perpendicular to the sheet surface of FIG. 5).

If the side surface of the color filter protrudes outward (towards the boundary portion) of the light guide portion from the side surfaces of the upper and lower portions of the light guide portion 505, even the light entering the boundary portion 506 may not enter the light guide portion, reducing the light collection coefficient. The side surface of the color filter protrudes outward (towards the boundary portion) of the light guide portion from the side surfaces of the upper and lower portions of the light guide portion when the color filter is larger in transverse width than the light guide portion when viewed from above (in a direction perpendicular to the sheet surface of FIG. 5 )

A two-dimensional ratio between the lens 501 and the light guide portion 505 will be explained with reference to FIG. 6. FIG. 6 is a plan view showing an arrangement of photosensitive surfaces 103 of photoelectric conversion elements, pixels 601 including photoelectric conversion elements, lenses 501, and light guide portions 505. The lower surface 501a of the lens 501 is larger than the upper surface 504a or the lower surface 502b light guide portion 505 (see FIG. 6). In this structure, the lens 501 can focus the light collected by the light guide portion 505 onto the photosensitive surface 103 (as indicated by the dashed line) without any loss. The lens 501 is made of a material having a higher refractive index than that of the light guide portion 505, and is a convex lens. However, when the refractive index of the lens 501 is lower than that of the light guide portion 505, the lens 501 may also be a concave lens. The material and shape of lens 501 can be appropriately selected.

Seen in perspective from a direction perpendicular to the photosensitive surface 103, the photosensitive photoelectric conversion element surface 103 is included in the lower surface 501a of the lens 501 (located inside) and is included in the upper surface 504a and the lower surface 502b of the light guide portion 505 (located inside).

7A-7F of FIG. 7 show a method of manufacturing a photoelectric conversion device 5 according to a second embodiment.

In step 7A of FIG. 7, foreign ions of the first type of conductivity are embedded in the substrate 100, forming a channel 101 in the substrate 100. Next, foreign ions of the second type of conductivity are embedded in a predetermined region of the substrate 100, forming photoelectric conversion elements 102 placed around the channel 101 in the substrate one hundred.

Then, an insulating film 104a is formed on the substrate 100. A wiring layer 105 is formed on the insulating film 104a. An insulating film 104b is formed to cover the insulating film 104a and the wiring layer 105.

The required number of insulating films and wiring layers are installed on top of each other.

Lenses 501 are formed on the insulating film 104b. Lens 501 is formed, for example, from silicon nitride.

In step 7B of FIG. 7, a smoothing layer 701 is formed to cover the lenses 501. The smoothing layer 701 has a flat upper surface. The smoothing layer 701 and color filters 702 are formed, for example, from polymer.

On the smoothing layer 701, red (R), green (G) and blue (B) filters 702 are formed. Color filters 702 are formed, for example, from polymer.

In step 7C of FIG. 7, a transparent film 703 serving as light guide sections is formed on the color filters 702. The transparent film 703 may be made, for example, of silicon oxide. It is desirable to form silicon oxide, for example, by the spin-on glass method (impurity shutters), which allows the formation of silicon oxide at low temperature so as not to spoil the semiconductor elements, lenses and color filters that are already formed.

In step 7D of FIG. 7, an etching mask 704 is formed on the transparent film 703. An etching mask 704 is formed by structuring the photoresist in accordance with the sample (see FIG. 6) of the light guide sections 505 by the photolithography method.

In step 7E of FIG. 7, the transparent film 703 is etched using an etching mask 704 to form the upper portions 504 of the light guide portions 505. When the transparent film is made of silicon oxide, anisotropic etching is performed using gaseous CF.

In step 7F of FIG. 7, to complete the light guide sections 505, the color filter layer 702 and the smoothing layer 701 are etched. According to the etching method, anisotropic etching is performed using an oxygen-containing gas, which removes part of the color filter layer and smooths it. As a result, color filters 503 and lower portions 502 of the light guide portions 505 are formed. At the same time, the etching mask 704 formed on the transparent film 703 is also etched. A lens 501 formed from silicon nitride can also act as an etch stop layer.

Further, microlenses (not shown) and the like are formed in the light guide portions 505.

Thus, the photoelectric conversion device 5 according to the second embodiment is formed.

The second embodiment provides for the use of color filters of primary colors (R, G and B). Therefore, the gap between the light guide sections (i.e., the width of the boundary section) and the height of the light guide section can be designed in accordance with the characteristics of the color filters of the respective colors, as described in the first embodiment. For example, the smallest wavelength in the wavelength range at which the light passing through the blue filter shows an intensity of half the peak value is specified as the smallest wavelength in the wavelength range of visible light. The longest wavelength in the wavelength range at which light passing through the red filter shows an intensity of half the peak value is specified as the longest wavelength in the wavelength range of visible light. Based on these settings, a gap is established between the light guide sections and the height of the light guide section.

In the second embodiment, the smoothing layer is placed under the color filter, but this is not always necessary. In the absence of a smoothing layer, the interface between different media in the fiber section can be eliminated, reducing internal reflection. As described above, according to the manufacturing method according to the second embodiment, the photoelectric conversion device with high light collection efficiency can be manufactured in a simple manner using semiconductor processing. This manufacturing method is also applicable to other embodiments.

(Third Embodiment)

The third embodiment is characterized in that the low-pass filter as an optical element is placed on the light guide sections. FIG. 8 is a cross-sectional view of the photoelectric conversion device 8 according to the third embodiment. The same positions as in FIG. 1 indicate the same details, and we will not repeat their description.

8, lenses 801 are formed on an insulating film 104b, and light guide portions 802 are formed on lenses 801. The detailed structure of the light guide portion 802 is the same as in the first embodiment, and we will not repeat its description. A low-pass filter 803 is located in the light guide sections 802.

Traditionally, when placing a low-pass filter in the photoelectric conversion device, even taking into account the light collection coefficient, a fiber optic plate (FOP) must be placed between the photoelectric conversion device and the low-pass filter. It is also necessary to place the microlens on the photoelectric conversion device and place the smoothing layer between the microlens and the low-pass filter.

In contrast, the upper surface of the light guide portion 802 is flat in the photoelectric conversion device 8 according to the third embodiment, therefore, the low-pass filter 803 can be placed on the photoelectric conversion element without the mediation of the FOP or smoothing layer. Since the interfaces formed by the placement of the FOP and the smoothing layer may disappear, light reflection at the interfaces can be prevented.

A third embodiment provides for the use of a low pass filter as an optical element. Other examples of an optical element are a wavelength converter, a plano-convex lens, a plano-concave lens, and a color filter. These optical elements can also be properly combined and stacked on top of each other. This structure facilitates installation. Since the optical element can be placed near the photoelectric conversion element, the light collection coefficient can be increased, and the aberration can also be reduced.

(Application to imaging system)

Fig. 9 is a block diagram illustrating the application of the photoelectric conversion device described according to Embodiments 1 through 3 of the present invention to an image forming system. The imaging system is, for example, a digital camera or video camera.

As shown in FIG. 9, the image forming system 90 mainly comprises an optical system, an image pickup device 904, and a signal processing unit. The optical system basically comprises a shutter 901, a lens 902 and an aperture 903. The image pickup device 904 includes a photoelectric conversion device 1 (or 5 or 8). The signal processing unit mainly comprises a received signal processing circuit 905, an A / D converter 906, an image signal processor 907, a memory 910, an external interface 913, a clock generator 908, a general control / arithmetic unit 909, an information storage medium 912, and a media management interface 911 information. The signal processing unit may not contain information carrier 912.

A shutter 901 is placed in front of the lens 902 on the optical path to control exposure.

The lens 902 refracts the incident light, forming an image of the object on the image sensing plane of the photoelectric conversion device 1 in the image sensing device 904.

Aperture 903 is located between the lens 902 and the photoelectric conversion device 1 on the optical path and controls the amount of light directed to the photoelectric conversion device 1 after passing through the lens 902.

The photoelectric conversion device 1 of the image pickup device 904 converts an image of an object formed on the image sensing plane of the photoelectric conversion device 1 into an image signal. The image pickup device 904 reads an image signal from the photoelectric conversion device 1 and outputs it.

The sensed signal processing circuitry 905 is connected to the image pickup device 904 and processes the image signal output from the image pickup device 904.

An A / D converter 906 is connected to the received signal processing circuitry 905 and converts the processed image signal (analog signal) output from the received signal processing circuitry 905 to an image signal (digital signal).

The image signal processor 907 is connected to the A / D converter 906 and performs various arithmetic processes, for example, correction of the image signal (digital signal) output from the A / D converter 906, generating image data. An image signal processor 907 transmits image data to a memory 910, an external interface 913, a general control / arithmetic unit 909, a storage medium control interface 911, and the like. in accordance with the setting (instruction) of the operating mode received by the general control / arithmetic unit 909 from the user through an input device (for example, a shutter button).

A memory 910 is connected to the image signal processor 907 and stores (stores) image data output from the image signal processor 907.

An external interface 913 is connected to the image signal processor 907. The external interface 913 may transmit image data output from the image signal processor 907 to an external device, such as a computer or printer.

The storage medium 912 is removably connected to the media control interface 911. The storage medium 912 records image data output from the image signal processor 907 through the storage medium control interface 911.

The clock generator 908 is connected to an image pickup device 904, a sensed signal processing circuit 905, an A / D converter 906, and an image signal processor 907. The clock generator 908 transmits the clock signals to the image pickup device 904, the received signal processing circuitry 905, the A / D converter 906, and the image signal processor 907. The image pickup device 904, the received signal processing circuitry 905, the A / D converter 906, and the image signal processor 907 operate in synchronization with the clock signals.

The general control / arithmetic unit 909 is connected to and controls all of them by a clock 908, an image signal processor 907, and a storage medium control interface 911.

An image pickup device 904, including a photoelectric conversion device 1 and an A / D converter 906, can also be formed on a single substrate (substrate 100 in FIG. 1), or can also be formed in one step. An image pickup device 904, including a photoelectric conversion device 1 and other constituent elements of the image forming system 90, can also be formed on a single substrate, and can also be formed in one step.

When the photoelectric conversion device according to the present invention is used in the image forming system, the number of mounted components to accommodate a low-pass filter and the like. can be shortened. A compact imaging system can be manufactured.

As described above, the present invention allows the manufacture of a photoelectric conversion element that increases the light collection coefficient.

Although the present invention has been described with reference to illustrative embodiments, it should be understood that the invention is not limited to the disclosed illustrative embodiments. The scope of the following claims is accorded the broadest interpretation, embracing all such modifications and equivalent structures and functions. The above embodiments may also be combined with each other.

This application claims the priority of Japanese patent application No. 2007-259874, filed October 3, 2007, which, therefore, is fully incorporated herein by reference.

Claims (15)

1. The photoelectric conversion device, characterized in that it contains
many photoelectric conversion elements, each of which has a photosensitive surface,
insulating films placed on a plurality of photoelectric conversion elements,
a plurality of light guide portions arranged on top of the insulating films, each of the plurality of light guide portions directing light onto the photosensitive surface of the photoelectric conversion element from the plurality of photoelectric conversion elements, and
boundary sections, each of the boundary sections defining a boundary between adjacent light guide sections and is made of a material having a lower refractive index than the material of which the plurality of light guide sections consists,
in which the width of each of the boundary sections does not exceed half the smallest wavelength in the wavelength range of visible light, and
the height from the lower surface to the upper surface of each of the plurality of light guide sections is not less than twice the largest wavelength in the wavelength range of visible light. 2. The device according to claim 1, characterized in that it further comprises a plurality of lenses located between the insulating films and the plurality of light guide sections. 3. The device according to claim 2, in which
each lens is made of silicon nitride, and
each of the plurality of light guide sections is made of silicon oxide. 4. The device according to claim 1, in which
the upper surfaces of the plurality of light guide sections are flush with each other and are flat. 5. The device according to claim 4, characterized in that it further comprises a low-pass filter located on a variety of light guide sections. 6. The device according to claim 1, characterized in that it further comprises a plurality of color filters placed over a plurality of photoelectric conversion elements. 7. The device according to claim 6, in which
each of the many color filters is part of the light guide section. 8. The device according to claim 6, in which
color filters are primary color filters, the smallest wavelength in the wavelength range of visible light is equal to the wavelength determined by the transmission spectral distribution of the blue filter, and
the longest wavelength in the wavelength range of visible light is equal to the wavelength determined by the spectral distribution of the transmission of the red filter. 9. The device according to claim 1, in which
the width of each boundary portion is not more than 0.2 μm, and
the height from the lower surface to the upper surface of each of the plurality of light guide portions is not less than 1.5 μm. 10. A photoelectric conversion device, characterized in that it contains many photoelectric conversion elements, each of which has a photosensitive surface,
insulating films placed on a plurality of photoelectric conversion elements,
a plurality of light guide sections arranged on top of insulating films of several layers, each of the plurality of light guide sections directing light to a photosensitive surface of the photoelectric conversion element from the plurality of photoelectric conversion elements, and
boundary sections, each of the boundary sections defining a boundary between adjacent light guide sections and is made of a material having a lower refractive index than the material of which the plurality of light guide sections consists,
in which the width of each of the boundary sections does not exceed half the smallest wavelength in the wavelength range of visible light, and
the height from the lower surface to the upper surface of each of the many light guide sections is not less than four times the width of each of the boundary sections. 11. The photoelectric conversion device, characterized in that it contains
many photoelectric conversion elements, each of which has a photosensitive surface,
a plurality of light guide sections arranged on top of the plurality of photoelectric conversion elements, each of which corresponds to a photoelectric conversion element of the plurality of photoelectric conversion elements, and
boundary sections, each of the boundary sections defining a boundary between adjacent light guide sections and is made of a material having a lower refractive index than the material of which the plurality of light guide sections consists,
in which the width of each of the boundary sections does not exceed half the smallest wavelength in the wavelength range of visible light, and
the height from the lower surface to the upper surface of each of the plurality of light guide sections is not less than twice the largest wavelength in the wavelength range of visible light. 12. An imaging system, characterized in that it contains a photoelectric conversion device according to any one of claims 1 to 11, an optical system that generates an image on the image perception plane of the photoelectric conversion element, and a signal processing unit that processes the signal output from the photoelectric device conversion, to generate image data. 13. The device according to any one of claims 1 to 11, in which
the wavelength range of visible light includes a wavelength range from 400 nm to 750 nm. 14. The device according to any one of claims 6 to 8, in which the shortest wavelength and longest wavelength in the wavelength range of visible light are determined, respectively, by the spectral distribution of the transmission of the color filter. 15. The device according to any one of claims 1 to 11, in which
multiple layers of insulating films are arranged on a plurality of photoelectric conversion elements, and
many light guide sections are placed on top of multiple layers of insulating films.

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